Fix shutdown method again and remove wait argument. Reduce PEP8 findings
1.2.10
Fix join method. Call shutdown method with the correct parameters. In shutdown method send finish command to child threads if soon is True independent of the wait parameter.
1.2.9
Add method join. Fix method shutdown_children to release job_cnt semaphore.
1.2.8
Fix global Shutdown method and add option 'now'.
1.2.7
Fix checking of type parameter wait in as_completed.